Essentially it is known that a thermal magnetic circuit breaker is a manually or automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and interrupt current flow. Therefore, the thermal magnetic circuit breaker has for example at least one magnetic trip device in order to prevent the electrical circuit or an electrical device from damage by short circuit and a thermal trip device in order to prevent the electric circuit or an electrical device from damage by overload. A short circuit is an abnormal connection between two nodes of the electric circuit intended to be at different voltages. And especially in reference to a molded-case circuit breaker, a short-circuit is an abnormal connection between two separate phases, which are intended to be isolated or insulated from each other. This results in an excessive electric current, named an overcurrent limited only by the Thévenin equivalent resistance of the rest of the network and potentially causes circuit damage, overheating, fire or explosion. An overload is a less extreme condition but a longer-term over-current condition as a short circuit.
The magnetic trip device has at least an armature element moveable arranged with respect to a yoke or especially to a current conduction element conducting electrical energy or current, respectively. The armature element or armature, respectively, is a magnetic element and especially a pole piece having at least partially an iron material and reacting to a magnetic field created by the yoke during a trip moment. In order to realize a guided movement of the armature element towards the yoke at least during a trip event like a short circuit, the armature element is arranged at an armature locator. The armature locator is moveable arranged at a pin extending from an adjustment bar towards the yoke. The armature locator or the adjustment bar is connectable with a trip bar, which is able to interrupt a current flow of the current circuit, when the trip bar is moved. For example, the trip bar is moved due to a movement of the armature locator or the adjustment bar in conjunction with the armature element towards the yoke because of a magnetic force.
Thermal magnetic circuit breakers are classified for example by different rated currents or tripping characteristics and/or according to the resistance to unwanted tripping due to transient voltages and the time delay in the presence of a residual current. In order to calibrate a translational magnetic system of a thermal magnetic circuit breaker it is known to use an adjustment screw inserted into the magnetic trip device through a bottom of the magnetic trip device and therefore through the yoke. The calibration via the bottom of the magnetic trip device is a less preferred access point, because additional calibration elements are needed and calibration is time-consuming and cost-intensive. In the context of the invention, calibration means a checking of the magnetic trip device against a reference, and a determining of and perhaps a minimising of the difference. That means that different measurements are compared, wherein one measurement is of known magnitude or correctness made or set with one device and another measurement is made in a similar way (as possible) with a second device.